Apparatus and method for supporting session continuity in wireless communication system

ABSTRACT

A method performed by a user equipment (UE) in a wireless communication system is provided. The method includes transmitting, to an access and mobility function (AMF), a registration request message for moving to a first public land mobile network (PLMN) from a second PLMN, receiving, from the AMF, a registration accept message including first single-network slice selection assistance information (S-NSSAI) corresponding to the first PLMN of the AMF, determining whether second S-NSSAI associated with a protocol data unit (PDU) session established for the UE matches to the first S-NSSAI, wherein the second S-NSSAI corresponds to the second PLMN, and locally updating the PDU session based on a result of the determining.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is based on and claims priority under 35 U.S.C. §119(a) of a Korean patent application number 10-2019-0053245, filed onMay 7, 2019, in the Korean Intellectual Property Office, the disclosureof which is incorporated by reference herein in its entirety.

BACKGROUND 1. Field

The disclosure relates to an apparatus and method for supporting sessioncontinuity in a wireless communication system.

2. Description of Related Art

In order to meet the demand with respect to wireless data traffic, whichis explosively increasing due to the commercialization of the 4^(th)generation (4G) communication system, an improved 5^(th) generation (5G)communication system or pre-5G communication system has been developed.For this reason, the 5G communication system or the pre-5G communicationsystem is called a beyond 4G network communication system or a post-longterm evolution (LTE) system.

To achieve a high data rate, the implementation of the 5G communicationsystem in an ultra-high-frequency millimeter wave (mmWave) band, forexample, a 60 GHz band, has been considered. In order to mitigate pathloss of radio waves and increase a transmission distance of radio wavesin the ultra-high frequency band, beamforming, massive multiple inputmultiple output (MIMO), full dimensional MIMO (FD-MIMO), array antenna,analog beam-forming, and large scale antenna techniques are beingdiscussed in regard to the 5G communication system.

Further, for improvement of a system network, in the 5G communicationsystem, technologies such as evolved small cells, advanced small cells,a cloud radio access network (cloud RAN), an ultra-dense network,device-to-device communication (D2D), wireless backhaul, a movingnetwork, cooperative communication, coordinated multi-points (CoMP),reception interference cancellation, and the like, have been developed.

In addition, in the 5G system, hybrid frequency shift keying andquadrature amplitude modulation (FQAM) and sliding window superpositioncoding (SWSC), which are advanced coding modulation (ACM) methods, andfilter bank multi-carrier (FBMC), non-orthogonal multiple access (NOMA),and sparse code multiple access (SCMA), which are advanced accesstechniques, are also being developed.

At the same time, the Internet has evolved from a human-centeredconnection network where humans create and consume information, to anInternet of Things (IoT) network where pieces of information areexchanged and processed among distributed components such as things.Internet of Everything (IoE) technology, in which big data processingtechnology through a connection to a cloud server and the like iscombined with the IoT technology, is also emerging. In order toimplement the IoT, technical components such as sensing technology,wired/wireless communication and network infrastructure, serviceinterface technology, and security technology are required. Recently, asensor network, machine-to-machine (M2M) communication, machine-typecommunication (MTC), and the like, for connection between things arebeing studied. In the IoT environment, intelligent Internet technology(IT) services that create new values in human life by collecting andanalyzing data generated from connected things may also be provided. TheIoT may be applied to fields such as smart homes, smart buildings, smartcities, smart cars or connected cars, smart grids, health care, smarthome appliances, advanced medical services, and the like, through fusionand convergence of existing IT technology and various industries.

Accordingly, various attempts have been made to apply the 5Gcommunication system to the IoT network. For example, technologies suchas a sensor network, M2M communication, MTC, and the like, are beingimplemented by the 5G communication technologies such as beamforming,MIMO, array antennas, and so forth. The use of the cloud RAN as theabove-mentioned big data processing technology is an example of theconvergence of the 5G technology and the IoT technology.

As various services are provided based on the above description andaccording to the development of a mobile communication system, there isdemand for a method to effectively provide services for supportinginterworking of, particularly, the 5G system (5GS) and an evolved packetsystem (EPS).

The above information is presented as background information only, andto assist with an understanding of the disclosure. No determination hasbeen made, and no assertion is made, as to whether any of the abovemight be applicable as prior art with regard to the disclosure.

SUMMARY

Aspects of the disclosure are to address at least the above-mentionedproblems and/or disadvantages, and to provide at least the advantagesdescribed below. Accordingly, an aspect of the disclosure is to providean apparatus and method for supporting session continuity in a wirelesscommunication system.

Additional aspects will be set forth in part in the description whichfollows and, in part, will be apparent from the description, or may belearned by practice of the presented embodiments of the disclosure.

In accordance with an aspect of the disclosure, a method performed by auser equipment (UE) in a wireless communication system is provided. Themethod includes transmitting, to an access and mobility function (AMF),a registration request message for moving to a first public land mobilenetwork (PLMN) from a second PLMN, receiving, from the AMF, aregistration accept message including first single-network sliceselection assistance information (S-NSSAI) corresponding to the firstPLMN of the AMF, determining whether second S-NSSAI associated with aprotocol data unit (PDU) session established for the UE matches to thefirst S-NSSAI, wherein the second S-NSSAI corresponds to the secondPLMN, and locally updating the PDU session based on a result of thedetermining.

In accordance with another aspect of the disclosure, the first S-NSSAIincludes a first slice/service type (SST) of the first PLMN and a firstmapped home PLMN (HPLMN) SST, the second S-NSSAI includes a secondmapped HPLMN SST, and the locally updating of the PDU session based onthe result of the determining comprises locally updating the secondS-NSSAI associated with the PDU session to the first S-NSSAIcorresponding to the first PLMN of the AMF based on the result of thedetermining.

In accordance with another aspect of the disclosure, the determining ofwhether the second S-NSSAI matches to the first S-NSSAI comprisesdetermining whether the first mapped HPLMN SST and the second mappedHPLMN SST are the same.

In accordance with another aspect of the disclosure, the first S-NSSAIfurther includes a first slice differentiator (SD) of the first PLMN anda first mapped HPLMN SD, the second S-NSSAI further includes a secondmapped HPLMN SD, and the determining of whether the second S-NSSAImatches to the first S-NSSAI further comprises determining whether thefirst mapped HPLMN SD and the second mapped HPLMN SD are the same.

In accordance with another aspect of the disclosure, the PDU session isused continuously and is not released by locally updating the secondS-NSSAI to the first S-NSSAI based on the result of the determining.

In accordance with another aspect of the disclosure, a method performedby an AMF in a wireless communication system is provided. The methodincludes receiving, from a user equipment (UE), a registration requestmessage for moving to a first PLMN from a second PLMN, and transmitting,to the UE, a registration accept message including first S-NSSAIcorresponding to the first PLMN of the AMF, wherein second S-NSSAIassociated with a PDU session established for the UE is locally updatedto the first S-NSSAI based on determining whether the first S-NSSAImatches to the second S-NSSAI, and wherein the second S-NSSAIcorresponds to the second PLMN.

In accordance with another aspect of the disclosure, the first S-NSSAIincludes a first SST of the first PLMN and a first mapped HPLMN SST, andthe second S-NSSAI includes a second mapped HPLMN SST.

In accordance with another aspect of the disclosure, the second S-NSSAIconfigured for the PDU session is locally updated to the first S-NSSAIin case that the first mapped HPLMN SST and the second mapped HPLMN SSTare the same.

In accordance with another aspect of the disclosure, the first S-NSSAIfurther includes a first SD of the first PLMN and a first mapped HPLMNSD, wherein the second S-NSSAI further comprises a second mapped HPLMNSD, and wherein the second S-NSSAI configured for the PDU session islocally updated to the first S-NSSAI in case that the first mapped HPLMNSD and the second mapped HPLMN SD are the same.

In accordance with another aspect of the disclosure, the PDU session isused continuously and not released by local update of the second S-NSSAIto the first S-NSSAI based on the result of the determining.

In accordance with another aspect of the disclosure, a user equipment(UE) in a wireless communication system is provided. The UE includes atransceiver, and at least one processor operably connected with thetransceiver and configured to transmit, to an AMF, by controlling thetransceiver, a registration request message for moving to a first publicland mobile network (PLMN) from a second PLMN, receive, from the AMF, bycontrolling the transceiver, a registration accept message includingfirst S-NSSAI corresponding to the first PLMN of the AMF, determinewhether second S-NSSAI associated with a PDU session established for theUE matches to the first S-NSSAI, wherein the second S-NSSAI correspondsto the second PLMN, and locally update the PDU session based on a resultof the determining.

In accordance with another aspect of the disclosure, an AMF in awireless communication system is provided. The AMF includes atransceiver, and at least one processor operably connected with thetransceiver and configured to receive, from a UE, by controlling thetransceiver, a registration request message for moving to a first publicland mobile network (PLMN) from a second PLMN, and transmit, to the UE,by controlling the transceiver, a registration accept message includingfirst S-NSSAI corresponding to the first PLMN of the AMF, wherein secondS-NSSAI associated with a PDU session established for the UE is locallyupdated to the first S-NSSAI based on determining whether the firstS-NSSAI matches to the second S-NSSAI, and wherein the second S-NSSAIcorresponds to the second PLMN.

Other aspects, advantages, and salient features of the disclosure willbecome apparent to those skilled in the art from the following detaileddescription, which, taken in conjunction with the annexed drawings,discloses various embodiments of the disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features, and advantages of certainembodiments of the disclosure will be more apparent from the followingdescription taken in conjunction with the accompanying drawings, inwhich:

FIG. 1 illustrates an interworking architecture between a 5G system(5GS) and an evolved packet system (EPS) in a non-roaming situation,according to an embodiment of the disclosure;

FIG. 2 illustrates an interworking architecture between a 5GS and an EPSin a local breakout roaming situation, according to an embodiment of thedisclosure;

FIG. 3 illustrates an interworking architecture between a 5GS and an EPSin a home-routed roaming situation, according to an embodiment of thedisclosure;

FIG. 4 illustrates examples of information received by a user equipment(UE) from a source public land mobile network (PLMN) and informationreceived by the UE from a target PLMN, according to an embodiment of thedisclosure;

FIG. 5A illustrates a handover procedure from a source PLMN to a targetPLMN, performed by a UE, according to an embodiment of the disclosure;

FIG. 5B illustrates a handover procedure from a source PLMN to a targetPLMN, performed by a UE, according to an embodiment of the disclosure;

FIG. 6 illustrates a procedure for registration with a target PLMN whena UE moves from a source PLMN to the target PLMN, according to anembodiment of the disclosure;

FIG. 7 illustrates a Protocol Data Unit (PDU) session modificationprocedure to enable a UE, after having moved from a source PLMN to atarget PLMN, to continuously use a PDU session in the target PLMN,according to an embodiment of the disclosure;

FIG. 8 illustrates a UE configuration update procedure for a UE, afterhaving moved from a source PLMN to a target PLMN, to continuously use aPDU session in the target PLMN, according to an embodiment of thedisclosure;

FIG. 9 illustrates a method for a UE to provide session continuity,according to an embodiment of the disclosure;

FIG. 10 illustrates a configuration of a UE, according to an embodimentof the disclosure; and

FIG. 11 illustrates a configuration of a network entity, according to anembodiment of the disclosure.

Throughout the drawings, like reference numerals will be understood torefer to like parts, components, and structures.

DETAILED DESCRIPTION

The following description with reference to the accompanying drawings isprovided to assist in a comprehensive understanding of variousembodiments of the disclosure as defined by the claims and theirequivalents. It includes various specific details to assist in thatunderstanding, but these are to be regarded as merely exemplary.Accordingly, those of ordinary skill in the art will recognize thatvarious changes and modifications of the various embodiments describedherein can be made without departing from the scope and spirit of thedisclosure. In addition, descriptions of well-known functions andconstructions may be omitted for clarity and conciseness.

The terms used in the following description and claims are not limitedto the bibliographical meanings, but are merely used to enable a clearand consistent understanding of the disclosure. Accordingly, it shouldbe apparent to those skilled in the art that the following descriptionof various embodiments of the disclosure is provided for illustrationpurpose only, and not for the purpose of limiting the disclosure asdefined by the appended claims and their equivalents.

It is to be understood that the singular form “a,” “an,” and “the”include plural referents unless the context clearly dictates otherwise.Thus, for example, reference to “a component surface” includes referenceto one or more of such surfaces. Unless defined otherwise, all termsused herein including technical or scientific terms have the samemeanings as those generally understood by those of ordinary skill in theart to which the disclosure may pertain. The terms as those defined ingenerally used dictionaries are construed to have meanings matching thatin the context of related technology and, unless clearly definedotherwise, are not construed to be ideally or excessively formal. Insome cases, even the terms defined in the disclosure cannot beinterpreted to exclude embodiments of the disclosure.

In the below-described various embodiments of the disclosure, ahardware-based access method is described as an example. However, asvarious embodiments of the disclosure include technologies using bothhardware and software, various embodiments of the disclosure do notexclude a software-based access method.

In the following description, when detailed descriptions about relatedwell-known functions or structures are determined to make the disclosureunclear, the detailed descriptions will be omitted. The terms used inthe disclosure have been selected from currently widely used generalterms in consideration of the functions in the disclosure. However, theterms may vary according to the intention of one of ordinary skill inthe art, case precedents, and with the advent of new technologies.Accordingly, the terms used in the disclosure are defined based on theirmeanings in relation to the contents discussed throughout thespecification, not by their simple meanings.

Further, each element illustrated in the drawings may be exaggerated,omitted, or schematically illustrated for convenience of explanation andclarity. The illustrated size of each element does not substantiallyreflect its actual size. In each drawing, like or corresponding elementsare denoted by like reference numerals.

The advantages and features of the disclosure and a method to achievethem will be clarified with reference to the embodiments described indetail with the accompanying drawings. This disclosure may, however, beembodied in many different forms and should not be construed as limitedto the embodiments set forth herein. Rather, these embodiments areprovided so that this disclosure will be thorough and complete, and willfully convey the scope of the disclosure to one of ordinary skill in theart. Throughout the drawings, like reference numerals denote likeelements.

Throughout the disclosure, the expression “at least one of a, b or c”indicates only a, only b, only c, both a and b, both a and c, both b andc, all of a, b, and c, or variations thereof.

Examples of a terminal may include a user equipment (UE), a mobilestation (MS), a cellular phone, a smartphone, a computer, a multimediasystem capable of performing a communication function, or the like.

In the disclosure, a controller may also be referred to as a processoror at least one processor.

Throughout the specification, a layer (or a layer apparatus) may also bereferred to as an entity.

It will be understood that blocks of flowcharts and combinations offlowcharts may be performed by computer program instructions. Becausethese computer program instructions may be loaded into a processor of ageneral-purpose computer, a special-purpose computer, or anotherprogrammable data processing apparatus, the instructions, which areperformed by a processor of a computer or another programmable dataprocessing apparatus, create units for performing functions described inthe flowchart block(s). The computer program instructions may be storedin a computer-usable or computer-readable memory capable of directing acomputer or another programmable data processing apparatus to implementa function in a particular manner, and thus the instructions stored inthe computer-usable or computer-readable memory may also be capable ofproducing manufacturing items containing instruction units forperforming the functions described in the flowchart block(s). Thecomputer program instructions may also be loaded into a computer oranother programmable data processing apparatus, and thus, instructionsfor operating the computer or the other programmable data processingapparatus by generating a computer-executed process when a series ofoperations are performed in the computer or the other programmable dataprocessing apparatus may provide operations for performing the functionsdescribed in the flowchart block(s).

In addition, each block may represent a portion of a module, segment, orcode that includes one or more executable instructions for executingspecified logical function(s). It should also be noted that in someimplementations, functions mentioned in blocks may occur out of order.For example, two blocks illustrated successively may actually beexecuted substantially concurrently, or the blocks may sometimes beperformed in a reverse order according to the corresponding function.

As used herein, the term “unit” means a software component or hardwarecomponent such as a field-programmable gate array (FPGA) or anapplication-specific integrated circuit (ASIC), and performs a specificfunction. However, the term “unit” is not limited to software orhardware. The “unit” may be formed so as to be in an addressable storagemedium, or may be formed so as to operate one or more processors.Accordingly, for example, the term “unit” may refer to components suchas software components, object-oriented software components, classcomponents, and task components, and may include processes, functions,attributes, procedures, subroutines, segments of program code, drivers,firmware, micro codes, circuits, data, a database, data structures,tables, arrays, or variables. A function provided by the components and“units” may be associated with the smaller number of components and“units”, or may be divided into additional components and “units”.Further, the components and “units” may be embodied to reproduce one ormore central processing units (CPUs) in a device or security multimediacard. As used herein, the “unit” may include at least one processor.

Hereinafter, the disclosure relates to an apparatus and method forproviding a network slice in a wireless communication system. In detail,the disclosure describes technology to provide session mobility in amobile communication network system which provides a network slicefunction in a wireless communication system.

Hereinafter, in the description, terms used to identify a node, termsreferring to a signal, terms referring to a channel, terms referring tocontrol information, terms referring to network entities, termsreferring to a component of an apparatus, terms referring to messages,terms referring to an interface between network entities, termsreferring to various pieces of identification information, and the like,are exemplified for convenience of description. Accordingly, thedisclosure is not limited to the below-mentioned terms, and other termshaving the same technical meaning may be used therefor.

Further, although the disclosure describes various embodiments by usingterms used in some communication protocols, for example, the 3rdGeneration Partnership Project (3GPP), this is merely for convenience ofexplanation. Various embodiments of the disclosure may be applied toother communication systems by being easily modified.

As a post-long term evolution (LTE) future communication system, the 5Gcommunication system supports a service to simultaneously satisfyvarious requirements because various requirements by users and serviceproviders are freely reflected. Services considered for the 5Gcommunication system include enhanced mobile broadband (eMBB), massivemachine-type communication (mMTC), and ultra-reliability and low-latencycommunication (URLLC).

According to an embodiment, the eMBB may have a goal of providing anenhanced data rate faster than the data rate supported by the existingLTE, LTE-advanced (LTE-A), or LTE-A pro (LTE-Pro). For example, in the5G communication system, the eMBB may provide, in view of one basestation, a peak data rate of about 20 Gbps for downlinks and a peak datarate of about 10 Gbps for uplinks. Further, the 5G communication systemmay provide a peak data rate and simultaneously an increased userperceived data rate of a UE. To satisfy the requirements in the 5Gcommunication system may require an improvement of varioustransmission/reception technologies including an enhanced multi-inputmulti-output (MIMO) transmission technology. Further, while the currentLTE transmits signals using a maximum 20 MHz transmission bandwidth in a2 GHz band, in the 5G communication system, a frequency bandwidth of 20MHz or more is used in a frequency band of 3 to 6 GHz or 6 GHz or more,and thus the data rate required in the 5G communication system may besatisfied.

Simultaneously, in the 5G communication system, the mMTC is consideredto support applied services such as the Internet of Things (IoT). Inorder to efficiently provide the IoT, the mMTC may be required tosupport an access by a large number of UEs within a cell, improve a UEcoverage, improve battery life, and reduce UE costs. The IoT, which isattached to various sensors and various devices and provides acommunication function, is able to support a large number of UEs, forexample, 1,000,000 UEs/km², in the cell. Further, as the UE supportingthe mMTC is highly likely to be located in a shaded area that the cellcannot cover, such as the basement of a building, due to thecharacteristics of the service, a wider coverage may be requiredcompared to other services provided in the 5G communication system. A UEsupporting the mMTC is configured with a low-cost UE, and as it isdifficult to frequently exchange the battery of a UE, a battery lifetime such as 10 to 15 years may be required.

Finally, the URLLC, as a cellular-based wireless communication serviceused for a specific purpose (mission-critical), may be used for servicesused for remote control for a robot or a machinery, industrialautomation, unmanned aerial vehicles, remote health care, emergencyalerts, and so forth. Accordingly, communication provided by the URLLCmay have very low low-latency (ultra-low latency) and very highreliability (super reliability). For example, a service supporting theURLLC may satisfy an air interface latency of less than 0.5 millisecondsand simultaneously have a requirement of a packet error rate of 10⁻⁵ orless. Accordingly, for services that support the URLLC, the 5G systemmay be asked for design factors of providing a smaller transmit timeinterval (TTI) than other services and simultaneously allocating a wideresource in a frequency band to secure the reliability of acommunication link.

The three services considered in the above-described 5G communicationsystem, that is, the eMBB, the URLLC, and the mMTC, may be multiplexedand transmitted in one system. At this time, in order to satisfydifferent requirements of the respective services, differenttransmission/reception techniques and transmission/reception parametersmay be used among the services. However, the above-described mMTC,URLLC, and eMBB are only examples of different service types, andservice types to which the disclosure is applied are not limited to theabove-described examples.

Further, in the following description, an embodiment of the disclosureis described with an example of an LTE, LTE-A, LTE Pro or 5G (or nextgeneration mobile communication (NR)) system, but the embodiment of thedisclosure may also be applied to other communication systems havingsimilar technical backgrounds or channel types. Still further, theembodiment of the disclosure may be applied to other communicationsystems through some modifications thereof without departing from thescope of the disclosure based on the determination of a person of skillin the art.

In a 3GPP standard, 5G network system architecture and procedure arestandardized. Mobile communication operators may provide variousservices in a 5G network. In order to provide each service, the mobilecommunication operator needs to satisfy different service requirementsfor each service, for example, latency, a communication range, a datarate, a bandwidth, reliability, and so forth. To this end, the mobilecommunication operator may configure a network slice and allocatenetwork resources suitable for a specific service for each network sliceor for each set of network slices. The network resource may mean an NF(network function) or a logical resource provided by the NF or radioresource allocation of a base station.

For example, the mobile communication operator may configure a networkslice A to provide a mobile broadband service, configure a network sliceB to provide a vehicle communication service, and configure a networkslice C to provide an IoT service. That is, in the 5G network, acorresponding service may be provided on a network slice specialized forthe characteristics of each service. Single-network slice selectionassistance information (S-NSSAI) defined in the 3GPP may be used as adifferentiator for differentiating (or, identifying) network slices. Onepiece of S-NSSAI may be configured with a SST used in a home public landmobile network (PLMN) (HPLMN), a SD used in the HPLMN, the SST used in avisited PLMN (VPLMN), and the SD used in the VPLMN. Each SST and SDconstituting one piece of the S-NSSAI may or may not have a valuedepending on the situation.

The mobile communication operator may operate the 5G network and evolvedpacket system (EPS) (or called LTE) network together. A mobilecommunication UE may access the 5G network to use services and then moveto the EPS network. Alternatively, the mobile communication UE mayaccess the EPS network to use services and then move to the 5G network.

In the disclosure, an interworking method between a 5G network systemarchitecture for providing a network slice function and an EPS networksystem is defined. FIGS. 1, 2, and 3 illustrate interworkingarchitectures between a 5G system (5GS) and an EPS. The terms N1, N2 . .. , and so forth, shown around the line connecting each entity refer tocommunication interfaces.

Further, a network operation and a UE operation are defined so that a UEusing a communication service by establishing a session connection inthe EPS may use the service seamlessly even when moving to the 5GS.

FIG. 1 illustrates an interworking architecture between a 5GS and an EPSin a non-roaming situation, according to an embodiment of thedisclosure.

Referring to FIG. 1, the 5GS may include a NR base station, as referredto as a next generation radio access network (NG-RAN) 150, an access andmobility management function (AMF) 145, a session management function(SMF) of 120, a user plane function (UPF) of 125, a policy controlfunction (PCF) of 115, and a unified data management (UDM) of 110. TheEPS may include an E-UTRA base station (E-UTRAN) 140, a mobilitymanagement entity (MME) 135, a serving gateway (SGW) 130, a packetgateway-user plane (PGW-U) of 125, a packet gateway-control plane(PGW-C) of 120, a policy and charging rules function (PCRF) of 115, anda home subscriber server (HSS) of 110.

The UDM of 110 of the 5GS and the HSS of 110 of the EPS may be providedas one combo node. The SMF of 120 of the 5GS and the PGW-C of 120 of theEPS may also be provided as one combo node. A node of the UDM+the HSS of110 may store subscriber information of a UE. The UPF of 125 of the 5GSand the PGW-U of 125 of the EPS may be provided as one combo node. A UE155 may access the MME 135 of the EPS via the E-UTRA base station 140and use EPS network services. Further, the UE 155 may access the AMF 145of the 5GS via the NR base station 150 and use 5GS network services.

FIG. 2 illustrates an interworking architecture between a 5GS and an EPSin a local breakout roaming situation, according to an embodiment of thedisclosure.

Referring to FIG. 2, a UE 260 may access an MME 240 of the EPS via anE-UTRA base station 245 and use the EPS network services. Further, theUE 260 may access an AMF 250 of the 5GS via an NR base station 255 anduse the 5GS network services. In the interworking architecture betweenthe 5GS and the EPS in local breakout roaming, a node of a SMF+PGW-C 225may be located in the VPLMN. FIG. 2 is divided into an HPLMN and aVPLMN. In FIG. 2, the PCF+PCRF 115 of FIG. 1 is divided into anh-PCF+h-PCRF 215 in the HPLMN and a v-PCF+v-PCRF 220 in the VPLMN.Remaining features 210, 225, 230, and 235, correspond to features ofFIG. 1 and therefore, further descriptions are omitted.

FIG. 3 illustrates an interworking architecture between a 5GS and an EPSin a home-routed roaming situation, according to an embodiment of thedisclosure.

Referring to FIG. 3, a UE 370 may access an MME 335 of the EPS via anE-UTRA base station (E-UTRAN) 340 and use the EPS network services.Further, the UE 370 may access an AMF 360 of the 5GS via an NR basestation 365 and use the 5GS network services. In the interworkingarchitecture between the 5GS and the EPS in a home-routed roaming, anode of a SMF+PGW-C 320 may be located in the HPLMN. FIG. 3 is dividedinto an HPLMN and a VPLMN. In FIG. 3, the PCF+PCRF 115 of FIG. 1 isdivided into an h-PCF+h-PCRF 315 in the HPLMN and a v-PCF 345 in theVPLMN. A v-SMF 350 and a UPF are in the VPLMN. Remaining features 310,325, and 330, correspond to features of FIG. 1 and therefore, furtherdescriptions are omitted.

A mobile communication system according to an embodiment of thedisclosure may support interworking between the 5GS and the EPS. Forexample, the UE that accesses an EPS system and generates a public datanetwork or packet data network (PDN) connection (PDN connection) maymove or hand over to the 5GS and continuously use the PDN connectiongenerated in the EPS in the 5GS as a protocol data unit (PDU) session.

In detail, the SMF+PGW-C 120, 225, or 320 that received a PDNconnectivity request message transmitted by the UE having accessed theEPS system may select S-NSSAI for the PDN connection requested by theUE. The SMF+PGW-C 120, 225, or 320 may transmit to the UE by includingthe selected S-NS SAI information as protocol configuration options(PCO) in a PDN connectivity response message transmitted to the UE. TheUE having received the PDN connectivity response message establishes aPDN connection in the EPS and use the services. After moving to the 5GS,the UE may continuously use the PDN connection generated in the EPS as aPDU session in the 5GS, by using the S-NSSAI received from the SMF+PGW-C120, 225, or 320 of the EPS in the form of PCO. In the above-describedembodiments, the EPS may be referred to as the source PLMN, and the 5GSmay be referred to as the target PLMN.

Further, the 5G mobile communication system may support inter-PLMNmobility. For example, a UE that has registered with a PLMN A andgenerated a PDU session may hand over to a PLMN B and continuously usethe PDU session.

In detail, the UE having accessed a 5GS system of the PLMN A maydetermine S-NSSAI to be used in a PDU session based on a UE routeselection policy (URSP) information stored in the UE to make a PDUsession establishment. The UE may transmit to the SMF of 120 a PDUsession establishment request message including the selected S-NSSAI.The SMF of 120 having received the PDU session establishment requestmessage may store the S-NSSAI included in the request message andtransmit to the UE a PDU session establishment response. The UE havingreceived the PDU session establishment response message may establish aPDU session in the 5GS of the PLMN A and use services. After moving tothe 5GS of the PLMN B, the UE may continuously use the PDU sessiongenerated in the 5GS of the PLMN A in the 5GS of the PLMN B. Bycontinuously using the PDU session, when the UE moves from a source PLMNto a target PLMN, a procedure of releasing an established PDU sessionmay not be performed. In addition, by continuously using the PDUsession, when the UE moves from the source PLMN to the target PLMN, aprocedure of establishing a new PDU session different from theestablished PDU session may not be performed. That is, by updating thecontext of the established PDU session (e.g., S-NSSAI update) accordingto an embodiment of the disclosure, when the UE moves from the sourcePLMN to the target PLMN, the PDU session release and/or establishmentprocedure may be omitted. In the above-described embodiment, the 5GS ofthe PLMN A may be referred to as the source PLMN, and the 5GS of thePLMN B may be referred to as the target PLMN.

FIG. 4 illustrates examples of information received by a UE from asource PLMN and information received by a UE from a target PLMN,according to an embodiment of the disclosure.

Referring to FIG. 4, a UE may store S-NSSAI information for a PDNconnection or a PDU session generated from the source PLMN. The UE maystore the S-NSSAI as context information of the PDN connection or thePDU session. The S-NSSAI may include at least one of values used in anSST 400 used in the HPLMN, an SD 401 used in the HPLMN, an SST 405 usedin the VPLMN, or an SD 406 used in the VPLMN. When the UE generates aPDN connection in the EPC, the S-NSSAI may be S-NSSAI informationreceived from the SMF+PGW-C 120, 225, or 320 in the form of PCO.Alternatively, when the UE generates a PDU session in the 5GS, theS-NSSAI may be S-NSSAI information selected by the UE based on the URSPstored in the UE.

After moving to the target PLMN, the UE may receive from the target PLMNS-NSSAI to continuously move from PDN connection to PDU session by usingthe procedure illustrated in FIGS. 5A to 8. The S-NSSAI received by UEfrom the target PLMN may include at least one of values of an SST 410used in the HPLMN, an SD 411 used in the HPLMN, an SST 415 used in theVPLMN, or an SD 416 used in the VPLMN.

The UE may store the S-NSSAI information received from the target PLMNand update the context of the PDU session stored in the UE. For example,the UE may change the SST 400 used in the HPLMN to the SST 410 used inthe HPLMN which is received from the target PLMN. Further, the UE maychange the SD 401 used in the HPLMN to the SD 411 used in the HPLMNwhich is received from the target PLMN. Still further, the UE may changethe SST 405 used in the VPLMN to the SST 415 used in the VPLMN which isreceived from the target PLMN. Still further, the UE may change the SD406 used in the VPLMN to the SD 416 used in the VPLMN which is receivedfrom the target PLMN. When the UE does not receive from the target PLMNat least one piece of information about the SST 410 used in the HPLMN,the SD 411 used in the HPLMN, the SST 415 used in the VPLMN, or the SD416 used in the VPLMN, the UE may use, without change, at least onepiece of information about the SST 400 used in the HPLMN, the SD 401used in the HPLMN, the SST 405 used in the VPLMN, or the SD 406 used inthe VPLMN, which are stored as the context of the PDU session in thesource PLMN, or may configure a field of the information that is notreceived from the target PLMN as empty.

FIGS. 5A and 5B illustrate a handover procedure from a source PLMN to atarget PLMN, performed by a UE, according to various embodiments of thedisclosure.

Referring to FIG. 5A, an Nsmf_PDUSession_UpdateSMContext Responsemessage in operation 7 that an SMF 510 transmits to a target-AMF (T-AMF)505 may include S-NSSAI information for a PDU session. The S-NSSAIinformation may include at least one piece of information about the SST410 used in the HPLMN, the SD 411 used in the HPLMN, the SST 415 used inthe VPLMN, or the SD 416 used in the VPLMN. The T-AMF 505 that receivedthe S-NSSAI information for a PDU session from the SMF 510 may store thereceived S-NSSAI information and/or PDU session information related tothe S-NSSAI information.

A Namf_Communication_CreateUEContext Response message in operation 12transmitted by the T-AMF 505 to a source-AMF (S-AMF) 503 may include theS-NSSAI and/or the PDU session information that the T-AMF 505 receivedin operation 7 from the SMF 510. The S-AMF 503 that received the S-NSSAIinformation for a PDU session from the T-AMF 505 may store the receivedS-NSSAI information and/or PDU session information related to theS-NSSAI information.

Referring to FIG. 5B, the Handover Command messages in operations 1 and2 that the S-AMF 503 transmits to a UE 501 via a source-NG-RAN(S-NG-RAN) 502 may include the S-NSSAI and/or the PDU sessioninformation that the S-AMF 503 received from the T-AMF 505 through theprocedure illustrated in FIG. 5A. The UE 501 that received the S-NSSAIinformation for a PDU session from the S-AMF 503 may store the receivedS-NSSAI information and/or PDU session information related to theS-NSSAI information and update the relevant PDU session context.Operations 1, 2, 3, 4, 5, 6a, 6b, 6c, 6d, 8, 9, 10, 11a, 11b, 11c, 11d,11e, and 11f of FIG. 5A are described as shown in the drawing, andfurther descriptions are omitted. Operations 2a, 2b, 2c, 3a, 4, 5, 6a,6b, 6c, 7, 8a, 8b, 9a, 9b, 10a, 10b, 11, 12, 13a, 13b, 14a, 14b, 15a,and 15b of FIG. 5B are described as shown in the drawing, and furtherdescriptions are omitted.

FIG. 6 illustrates a procedure of registration with a target PLMN when aUE moves from a source PLMN to the target PLMN, according to anembodiment of the disclosure.

Referring to FIG. 6, A UE 601 may transmit a registration requestmessage to a new ANF 603 in operations 1-3. The UE 601 may transmit, tothe new AMF 603, the registration request message for moving to a targetPLMN from a source PLMN. The UE 601 may transmit the registrationrequest message to the new AMF 603 via an (R)AN. AnNsmf_PDUSession_UpdateSMContext to Nsmf_PDUSession_ReleaseSMContextmessage in operation 17 that an SMF 606 transmits to a new AMF 603,relative to an old AMF 604, may include S-NSSAI information for a PDUsession. The S-NSSAI information may include at least one piece ofinformation about the SST 410 used in the HPLMN, the SD 411 used in theHPLMN, the SST 415 used in the VPLMN, or the SD 416 used in the VPLMN.The new AMF 603 that received the S-NSSAI information for a PDU sessionfrom the SMF 606 may store the received S-NSSAI information and/or PDUsession information related to the S-NSSAI information. A PCF 605,authentication server function (AUSF) 607, and UDM 608 are shown, butnot described further.

A Registration Accept message in operation 21 that the new AMF 603transmits to a UE 601 via an (R)AN 602 may include the S-NSSAI and/orPDU session information that the new AMF 603 received from the SMF 606.The UE 601 that received the S-NSSAI information for a PDU session fromthe new AMF 603 may store the received S-NSSAI information and/or PDUsession information related to the S-NSSAI information and locallyupdate the relevant PDU session context. For example, the UE 601 maydetermine whether S-NSSAI associated with a PDU session, which isestablished for the UE 601 and not yet updated, matches to the receivedS-NSSAI for a PDU session received from the AMF 603, and may update theestablished PDU session based on a result of the determining. Operations1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14a, 14b, 14c, 14d, 14e, 15,16, 18, 19, 19a, 19b, 19c, 21b, 22, 23 and 24 of FIG. 6 are described asshown in the drawing, and further descriptions are omitted.

FIG. 7 illustrates a PDU session modification procedure to enable a UE,after having moved from a source PLMN to a target PLMN, to continuouslyuse a PDU session in the target PLMN, according to an embodiment of thedisclosure.

Referring to FIG. 7, an Nsmf_PDUSession_UpdateSMContext message inoperation 3a, a Namf_Communication_N1N2MessageTransfer message inoperation 3b, and a Nsmf_PDUSessionSMContextStatusNotify message inoperation 3c, which an SMF 704 transmits to an AMF 703, may includeS-NSSAI information for a PDU session. The S-NSSAI information mayinclude at least one piece of information about the SST 410 used in theHPLMN, the SD 411 used in the HPLMN, the SST 415 used in the VPLMN, orthe SD 416 used in the VPLMN. The AMF 703 that received the S-NSSAIinformation for a PDU session from the SMF 704 may store the receivedS-NSSAI information and/or PDU session information related to theS-NSSAI information. A PCF 707, UDM 706, and UPF 705 are shown, but notdescribed further.

An N2 Session Request message in operation 4 and an AN-specific resourcemodification message in operation 5 that the AMF 703 transmits to a UE701 via a RAN 702 may include the S-NSSAI and/or PDU session informationthat the AMF 703 received from the SMF 704. The UE 701 that received theS-NSSAI information for a PDU session from the AMF 703 may store thereceived S-NSSAI information and/or PDU session information related tothe S-NSSAI information and update the relevant PDU session context.Operations 1, 1a, 1b, 1c, 1d, 1e, 1f, 2, 2a, 2b, 6, 7a, 7b, 8a, 8b, 9,10, 11a, 11b, 12a, 12b, and 13 of FIG. 7 are described as shown in thedrawing, and further descriptions are omitted.

FIG. 8 illustrates a UE configuration update procedure for a UE, afterhaving moved from a source PLMN to a target PLMN, to continuously use aPDU session in the target PLMN, according to an embodiment of thedisclosure.

Referring to FIG. 8, an SMF 804 may trigger, in operation 0, to an AMF803 the UE configuration update procedure. The SMF 804 may transmit tothe AMF 803 the S-NSSAI information for a PDU session and/or PDU sessioninformation. The S-NSSAI information may include at least one piece ofinformation about the SST 410 used in the HPLMN, the SD 411 used in theHPLMN, the SST 415 used in the VPLMN, or the SD 416 used in the VPLMN.The AMF 803 that received the S-NSSAI information for a PDU session fromthe SMF 804 may store the received S-NSSAI information and/or PDUsession information related to the S-NSSAI information. A UDM 805 isshown, but not described further.

A UE Configuration Update Command message in operation 1 that the AMF803 transmits to a UE 801 via an (R)AN 802 may include the S-NSSAIand/or PDU session information that the AMF 803 received from the SMF804. The UE 801 that received the S-NSSAI information for a PDU sessionfrom the AMF 803 may store the received S-NSSAI information and/or PDUsession information related to the S-NSSAI information and update therelevant PDU session context. Operations 2a, 2b, 2c, 2d, 3a, 3b, 3c, and4 of FIG. 8 are described as shown in the drawing, and furtherdescriptions are omitted.

The UE according to an embodiment of the disclosure may receive aRegistration Accept message in operation 21 of FIG. 6 through theprocedure illustrated in FIG. 6. The Registration Accept message mayinclude Allowed NSSAI and/or Mapping of Allowed NSSAI information thatthe UE may use in a corresponding PLMN. The Allowed NSSAI may includeone or more pieces of S-NSSAI that the UE may use in the PLMN and isprovided by a serving PLMN. The Mapping of Allowed NSSAI may include oneor more S-NSSAI that the UE may use in the PLMN and is provided by theserving PLMN and S-NSSAI information of the HPLMN that is mapped to eachS-NSSAI. Examples of the Allowed NSSAI and the Mapping of Allowed NSSAIare presented below.

{(HPLMN SST-A, HPLMN SD-A), (VPLMN SST-E, VPLMN SD-E)},

{(HPLMN SST-C, HPLMN SD-C), (VPLMN SST-D, VPLMN SD-D)},

{(HPLMN SST-F, HPLMN SD-F), (VPLMN SST-G, VPLMN SD-G)}

In a detailed description of the above-described examples, the UE mayaccess the serving PLMN and use three slices provided by the servingPLMN, that is, (VPLMN SST-E, VPLMN SD-E), (VPLMN SST-D, VPLMN SD-D), and(VPLMN SST-G, VPLMN SD-G). Slices of each VPLMN may be mapped to (HPLMNSST-A, HPLMN SD-A), (HPLMN SST-C, HPLMN SD-C), and (HPLMN SST-F, HPLMNSD-F).

The UE having received the Allowed NS SAI and the Mapping of AllowedNSSAI may compare the information in the source PLMN of FIG. 4 with theabove-described Allowed NSSAI and Mapping of Allowed NSSAI informationand produce available slice information for a PDU session in the targetPLMN. For example, referring to FIG. 4, the UE may compare the SST 400used in the HPLMN and/or the SD 401 used in the HPLMN that the UE storeswith the SST value used in the HPLMN and/or SD values used in the HPLMNreceived in operation 21 of FIG. 6. For example, {(HPLMN SST-A, HPLMNSD-A), (VPLMN SST-E, VPLMN SD-E)} that is a value of the Allowed NSSAIincluding HPLMN SST-A and HPLMN SD-A that are respectively a value ofthe SST 400 used in the HPLMN and a value of the SD 401 used in theHPLMN, which are stored in the UE, may be determined. The UE maydetermine the value of the VPLMN S-NSSAI mapped to the HPLMN S-NSSAI ofthe above-described Allowed NSSAI, that is, the VPLMN SST-E and VPLMNSD-E, as values of the SST 415 used in the target PLMN and the SD 416used in the target PLMN and update the relevant PDU session context. Theupdating of the relevant PDU session context may mean the determiningthe value of the VPLMN S-NSSAI mapped to the HPLMN S-NSSAI of theabove-described Allowed NSSAI, that is, the VPLMN SST-E and VPLMN SD-E,as values of the SST 415 used in the target PLMN and the SD 416 used inthe target PLMN.

FIG. 9 illustrates a method for a UE to provide session continuity,according to an embodiment of the disclosure.

Referring to FIG. 9, in operation 910, the UE may transmit, to an accessand mobility function (AMF), a registration request message for movingto a first public land mobile network (PLMN) from a second PLMN.

In operation 920, the UE may receive, from the AMF, a registrationaccept message comprising first single-network slice selectionassistance information (S-NSSAI) corresponding to the first PLMN of theAMF.

In operation 930, the UE may compare second S-NSSAI associated with aprotocol data unit (PDU) session established for the UE with the firstS-NSSAI, wherein the second S-NSSAI corresponds to the second PLMN.

In operation 940, the UE may locally update the PDU session based on aresult of the comparing.

FIG. 10 illustrates a configuration of a UE, according to an embodimentof the disclosure.

Referring to FIG. 10, a UE of the disclosure may include a transceiver1010, a memory 1020, and a processor 1030. The processor 1030, thetransceiver 1010, and the memory 1020 of the UE may operate according tothe above-described communication method of the UE. However, constituentelements of the UE are not limited to the above-description. Forexample, the UE may include constituent elements more or less than theabove-described constituent elements. In addition, the processor 1030,the transceiver 1010, and the memory 1020 may be implemented in the formof one chip. Further, the processor 1030 may include at least oneprocessor.

The transceiver 1010, which collectively refers to a receiver of the UEand a transmitter of the UE, may transceive signals with a base station.The signal transceived with the base station may include controlinformation and data. To this end, the transceiver 1010 may include anRF transmitter for up converting and amplifying the frequency oftransmitted signals and an RF receiver for low noise amplifying receivedsignal and down converting frequencies thereof. However, this is merelyone embodiment of the transceiver 1010, and the constituent elements ofthe transceiver 1010 are not limited to the RF transmitter and the RFreceiver.

Further, the transceiver 1010 may receive signals through a wirelesschannel and output the signals to the processor 1030, and transmit thesignals output from the processor 1030 through the wireless channel.

The memory 1020 may store programs and data needed for the operation ofthe UE. Further, the memory 1020 may store control information or dataincluded in the signals obtained by the UE. The memory 1020 may includestorage media such as ROM, RAM, hard disks, CD-ROMs, and DVDs, or acombination thereof.

The processor 1030 may control a series of processes so that the UEoperates according to the above-described embodiment of the disclosure.For example, the processor 1030 may receive control signals and datasignals through the transceiver 1010 and process the received controlsignals and data signals. Further, the processor 1030 may transmit theprocessed control signal and data signal to the transceiver 1010.

FIG. 11 illustrates a configuration of a network entity, according to anembodiment of the disclosure.

As illustrated in FIG. 11, a network entity of the disclosure mayinclude a transceiver 1110, a memory 1120, and a processor 1130. Theprocessor 1130, the transceiver 1110, and the memory 1120 of the networkentity may operate according to the above-described communication methodof the network entity. However, constituent elements of the networkentity are not limited to the above-description. For example, thenetwork entity may include constituent elements more or less than theabove-described constituent elements. In addition, the processor 1130,the transceiver 1110, and the memory 1120 may be implemented in the formof one chip. Further, the processor 1130 may include at least oneprocessor. Various network entities described in the disclosure (e.g.,AMF, SMF, base station, etc.) may correspond to the network entity ofFIG. 11.

The transceiver 1110, which collectively refers to a receiver of thenetwork entity and a transmitter of the network entity, may transceivesignals with a base station. The signal transceived with the basestation may include control information and data. To this end, thetransceiver 1110 may include an RF transmitter for up converting andamplifying the frequency of transmitted signals and an RF receiver forlow noise amplifying received signal and down converting frequenciesthereof. However, this is merely one embodiment of the transceiver 1110,and the constituent elements of the transceiver 1110 are not limited tothe RF transmitter and the RF receiver.

Further, the transceiver 1110 may receive signals through a wirelesschannel and output the signals to the processor 1130, and transmit thesignals output from the processor 1130 through the wireless channel.

The memory 1120 may store programs and data needed for the operation ofthe network entity. Further, the memory 1120 may store controlinformation or data included in the signals obtained by the networkentity. The memory 1120 may include storage media such as ROM, RAM, harddisks, CD-ROMs, and DVDs, or a combination thereof.

The processor 1130 may control a series of processes so that the networkentity operates according to the above-described embodiment of thedisclosure. For example, the processor 1130 may receive control signalsand data signals through the transceiver 1110 and process the receivedcontrol signals and data signals. Further, the processor 1130 maytransmit the processed control signal and data signal to the transceiver1110.

The methods according to the embodiments described in the claims orspecification of the disclosure may be implemented by hardware,software, or a combination of hardware and software.

When implemented by software, a computer-readable storage medium or acomputer program product for storing one or more programs (softwaremodules) may be provided. The one or more programs can be stored in anon-transitory computer-readable storage medium or computer programproduct and be configured for execution by one or more processors in anelectronic device. The one or more programs may include instructionswhich make the electronic device to execute the methods according to theembodiments described in the claims or specification of the disclosure.

Such programs (software modules, software) may be stored in non-volatilememory including random access memory or flash memory, read only memory(ROM), electrically erasable programmable read-only memory (EEPROM),magnetic disc storage devices, compact disc-ROM (CD-ROM), digitalversatile discs (DVDs), or other types of optical storage apparatuses ormagnetic cassettes. Alternatively, the programs may be stored in memoryincluding a combination of some or the whole thereof. Further, aplurality of constituent memories may be included.

Further, the programs may be stored in an attachable storage device thatis accessible via a communication network such as the Internet,Intranet, local area networks (LANs), wide LANs (WLANs), or storage areanetwork (SANs) communication networks, or a combination thereof. Thestorage apparatus may access an apparatus that performs an embodiment ofthe disclosure through an external port. Further, a separate storageapparatus on a communication network may access an apparatus thatperforms the embodiment of the disclosure.

In the above-described detailed embodiments of the disclosure, theconstituent element included in the disclosure is expressed in asingular form or a plural form according to the detailed embodiment.However, the singular or plural expression is selected as being suitablefor a given situation for the convenience of explanation, and thedisclosure is not limited to a singular or plural form of constituentelements. Even the plurally expressed constituent elements may becomposed of a single constituent element or vice versa.

According to an apparatus and method according to various embodiments ofthe disclosure, a mobile communication system may effectively provideservices by supporting continuity of a session in a mobile communicationnetwork system that provides a network slice function.

The effects that can be obtained from the disclosure are not limited tothe effects mentioned above, and other effects that are not mentionedcould be clearly understood by those of skill in the art to which thedisclosure pertains from the description below.

While, the disclosure has been shown and described with reference tovarious embodiments thereof, it will be understood by those skilled inthe art that various changes in form and detail may be made thereinwithout departing from the spirit and scope of the disclosure as definedby the appended claims and their equivalents.

Further, each embodiment can be operated in combination with each otheras necessary. For example, one embodiment of the disclosure and parts ofanother embodiment may be combined with each other. Still further, theembodiments may be implemented in other systems, for example, LTEsystems, 5G or NR systems, and other modified examples based on thetechnical concept of the above-described embodiment.

What is claimed is:
 1. A method performed by a user equipment (UE) in awireless communication system, the method comprising: transmitting, toan access and mobility function (AMF), a registration request messagefor moving to a first public land mobile network (PLMN) from a secondPLMN; receiving, from the AMF, a registration accept message comprisingfirst single-network slice selection assistance information (S-NSSAI)corresponding to the first PLMN of the AMF; determining whether secondS-NSSAI associated with a protocol data unit (PDU) session establishedfor the UE matches to the first S-NSSAI, wherein the second S-NSSAIcorresponds to the second PLMN; and locally updating the PDU sessionbased on a result of the determining.
 2. The method of claim 1, whereinthe first S-NSSAI comprises a first slice/service type (SST) of thefirst PLMN and a first mapped home PLMN (HPLMN) SST, wherein the secondS-NSSAI comprises a second mapped HPLMN SST, and wherein the locallyupdating of the PDU session based on the result of the determiningcomprises locally updating the second S-NSSAI associated with the PDUsession to the first S-NSSAI corresponding to the first PLMN of the AMFbased on the result of the determining.
 3. The method of claim 2,wherein the determining of whether the second S-NSSAI matches to thefirst S-NSSAI comprises determining whether the first mapped HPLMN SSTand the second mapped HPLMN SST are the same.
 4. The method of claim 3,wherein the first S-NSSAI further comprises a first slice differentiator(SD) of the first PLMN and a first mapped HPLMN SD, wherein the secondS-NSSAI further comprises a second mapped HPLMN SD, and wherein thedetermining of whether the second S-NSSAI matches to the first S-NSSAIfurther comprises determining whether the first mapped HPLMN SD and thesecond mapped HPLMN SD are the same.
 5. The method of claim 1, whereinthe PDU session is used continuously and not released by locallyupdating the second S-NSSAI to the first S-NSSAI based on the result ofthe determining.
 6. A method performed by an access and mobilityfunction (AMF) in a wireless communication system, the methodcomprising: receiving, from a user equipment (UE), a registrationrequest message for moving to a first public land mobile network (PLMN)from a second PLMN; and transmitting, to the UE, a registration acceptmessage comprising first single-network slice selection assistanceinformation (S-NSSAI) corresponding to the first PLMN of the AMF,wherein second S-NSSAI associated with a protocol data unit (PDU)session established for the UE is locally updated to the first S-NSSAIbased on determining whether the first S-NSSAI matches to the secondS-NSSAI, and wherein the second S-NSSAI corresponds to the second PLMN.7. The method of claim 6, wherein the first S-NSSAI comprises a firstslice/service type (SST) of the first PLMN and a first mapped home PLMN(HPLMN) SST, and wherein the second S-NSSAI comprises a second mappedHPLMN SST.
 8. The method of claim 7, wherein the second S-NSSAIconfigured for the PDU session is locally updated to the first S-NSSAIin case that the first mapped HPLMN SST and the second mapped HPLMN SSTare the same.
 9. The method of claim 8, wherein the first S-NSSAIfurther comprises a first slice differentiator (SD) of the first PLMNand a first mapped HPLMN SD, wherein the second S-NSSAI furthercomprises a second mapped HPLMN SD, and wherein the second S-NSSAIconfigured for the PDU session is locally updated to the first S-NSSAIin case that the first mapped HPLMN SD and the second mapped HPLMN SDare the same.
 10. The method of claim 6, wherein the PDU session is usedcontinuously and not released by local update of the second S-NSSAI tothe first S-NSSAI based on the result of the determining.
 11. A userequipment (UE) in a wireless communication system, the UE comprising: atransceiver; and at least one processor operably connected with thetransceiver and configured to: transmit, to an access and mobilityfunction (AMF), by controlling the transceiver, a registration requestmessage for moving to a first public land mobile network (PLMN) from asecond PLMN, receive, from the AMF, by controlling the transceiver, aregistration accept message comprising first single-network sliceselection assistance information (S-NSSAI) corresponding to the firstPLMN of the AMF, determine whether second S-NSSAI associated with aprotocol data unit (PDU) session established for the UE matches to thefirst S-NSSAI, wherein the second S-NSSAI corresponds to the secondPLMN, and locally update the PDU session based on a result of thedetermining.
 12. The UE of claim 11, wherein the first S-NSSAI comprisesa first slice/service type (SST) of the first PLMN and a first mappedhome PLMN (HPLMN) SST, wherein the second S-NSSAI comprises a secondmapped HPLMN SST, and wherein the at least one processor is furtherconfigured to locally update the second S-NSSAI associated with the PDUsession to the first S-NSSAI corresponding to the first PLMN of the AMFbased on the result of the determining.
 13. The UE of claim 12, whereinthe at least one processor is further configured to determine whetherthe first mapped HPLMN SST and the second mapped HPLMN SST are the same.14. The UE of claim 13, wherein the first S-NSSAI further comprises afirst slice differentiator (SD) of the first PLMN and a first mappedHPLMN SD, wherein the second S-NSSAI further comprises a second mappedHPLMN SD, and wherein the at least one processor is further configuredto determine whether the first mapped HPLMN SD and the second mappedHPLMN SD are the same.
 15. The UE of claim 11, wherein the PDU sessionis used continuously and not released by locally updating the secondS-NSSAI to the first S-NSSAI based on the result of the determining. 16.An access and mobility function (AMF) in a wireless communicationsystem, the AMF comprising: a transceiver; and at least one processoroperably connected with the transceiver and configured to: receive, froma user equipment (UE), by controlling the transceiver, a registrationrequest message for moving to a first public land mobile network (PLMN)from a second PLMN, and transmit, to the UE, by controlling thetransceiver, a registration accept message comprising firstsingle-network slice selection assistance information (S-NSSAI)corresponding to the first PLMN of the AMF, wherein second S-NSSAIassociated with a protocol data unit (PDU) session established for theUE is locally updated to the first S-NSSAI based on determining whetherthe first S-NSSAI matches to the second S-NSSAI, and wherein the secondS-NSSAI corresponds to the second PLMN.
 17. The AMF of claim 16, whereinthe first S-NSSAI comprises a first slice/service type (SST) of thefirst PLMN and a first mapped home PLMN (HPLMN) SST, and wherein thesecond S-NSSAI comprises a second mapped HPLMN SST.
 18. The AMF of claim17, wherein the second S-NSSAI configured for the PDU session is locallyupdated to the first S-NSSAI in case that the first mapped HPLMN SST andthe second mapped HPLMN SST are the same.
 19. The AMF of claim 18,wherein the first S-NSSAI further comprises a first slice differentiator(SD) of the first PLMN and a first mapped HPLMN SD, wherein the secondS-NSSAI further comprises a second mapped HPLMN SD, and wherein thesecond S-NSSAI configured for the PDU session is locally updated to thefirst S-NSSAI in case that the first mapped HPLMN SD and the secondmapped HPLMN SD are the same.
 20. The AMF of claim 16, wherein the PDUsession is used continuously and not released by local update of thesecond S-NSSAI to the first S-NSSAI based on the result of thedetermining.
 21. The method of claim 2, further comprising triggeringthe local updating of the PDU session in response to receiving S-NSSAIcomprising at least one piece of information about the first mappedHPLMN SST, an HPLMN slice differentiator (SD), a visited PLMN (VPLMN)SST, or a VPLMN SD.
 22. The method of claim 21, further comprisingstoring the received S-NSSAI.